In the next generation communication system, also known as the 4th Generation (4G) communication system, research is actively in progress to provide a Quality of Service (QoS) with a data transfer speed of about 100 Mbps. In particular, the 4 G communication system is currently being developed to ensure mobility and QoS in a Broadband Wireless Access (BWA) communication system, such as a Wireless Local Area Network (WLAN) system and a Wireless Metropolitan Area Network (WMAN) system. A representative example of such a communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
In the 802.16 system, a base station (BS) and a mobile station (MS) perform communication in a physical frame unit. The BS transmits a resource allocation message in every frame. By using the resource allocation message, the MS can know resources allocated to the MS within a frame. In this case, if there is an MS for receiving a service of which traffic is generated periodically or continuously, an unnecessary overhead is produced when resource allocation information is reported using the resource allocation message in every frame. To solve this problem, a scheme for fixedly allocating resources of a specific region in every frame is being considered, and this scheme is referred to as a fixed resource allocation scheme. That is, resources allocated using the fixed allocation scheme are used until the resources are changed or released.
In general, when using the fixed allocation scheme, radio resources are one-dimensionally represented. In other words, resources allocated to each of MSs are represented with a start-point offset and a duration. For example, if resources are allocated to five MSs according to the fixed allocation scheme, the resources are occupied as shown in FIG. 1A. Referring to FIG. 1A, slots 0 to 5 are allocated to an MS A, slots 6 to 9 are allocated to an MS B, slots 10 to 11 are allocated to an MS C, slots 12 to 17 are allocated to an MS D, slots 18 to 20 are allocated to an MS E, and slots 21 to 31 are unallocated.
If radio resources allocated to the MS C are released in a state of FIG. 1A, that is, if the slots 10 to 11 are released, locations of the slots allocated to the MS D and the MS E are implicitly changed as shown in FIG. 1B in order to prevent overall resources from being discontinuously allocated. That is, upon recognizing the release of the resources allocated to the MS C, the MS D and the MS E determine that the locations of the slots allocated to the MS D and the MS E are changed without receiving an additional message. Therefore, if a first MS allocated with resources according to the fixed allocation scheme cannot recognize the release of radio resources allocated to a second MS allocated with resources located prior to those of the first MS (for example, if the resource allocation message is not successfully received), the first MS operates abnormally. For example, if the MS D cannot recognize the release of the radio resources allocated to the MS C, the MS D attempts to receive a signal mapped to the slots 12 to 17. However, in this case, the BS transmits the signal to the MS D through the slots 10 to 15. Accordingly, the MS D cannot correctly receive the signal transmitted to the MS D, and as a result, a Cyclic Redundancy Check (CRC) error occurs. In a downlink scenario, when the release of the radio resources is not recognized, it affects only an MS that cannot recognize release of radio resources allocated to another MS. However, in an uplink scenario, other MSs are also affected. For example, if the MS D transmits a signal by mapping the signal onto the slots 12 to 17, collision occurs with a signal transmitted by the MS E and mapped onto the slots 16 to 17.
As described above, when the fixed allocation scheme is used in an implicit resource shifting scheme, if an MS unsuccessfully receives a resource allocation message, a resource allocation information disparity may occur between the MS and the BS. Accordingly, there is a need for a method of overcoming the resource allocation information disparity resulting from an unsuccessful reception of the resource allocation message.